Separation of alunite from associated rock and gangue.



UNITED STATES PATENT @ldtle CARL I HAGEIDORN, 01E CHICAGO, ILLINOIS, ASSIGNOR TU MINERAL PRODUCTET CORPORATION, OF NEW YDRK, N. IR, A CORPORATIQN 0F MAINE.

SEPARATION OF ALIJ'NITIE FROM ASSOCIATED JEWCIK AND C-i-AHQIS'FUE.

No Drawing.

To all whom it may concern:

Be it known that I, CARL F. HAcEooRN, a citizen of the United States, residing at Chicago, county of Cook, State of Illinois, have invented certain new and useful Improvements in Separation of Alunite from Associated Rock and Gangue; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

Alunite deposits, as found in nature, usually contain, interspersed therein, foreign material consisting of fragments of native rock, such as rhyolite. So also, when found in vein formation, the a'lunite is usually flanked on either side by disrupted or shattered native rock.

In the mining of the alunite, the native rock or rhyolite associated therewith appear together in the mined product, and are difficult of separation mechanically, for the reason that the specific gravity of the alunite is usually practically the same as that of the associated rock. The purpose of the present invention is to efiect a separation of the alunite constituent from the associated rock, by subjecting the mixture to a treatment which will produce a decided difference in the specific gravity of the constituents to be separated; whereupon their separation can be efi'ected by means readily available in the art.

In carrying out the invention the mined product is first roasted or calcined in such a way that the sulfuric acid combined with the alumina in the alunite is partially or wholly driven off. (The roasting or calcining operation does not materially change the specific.

gravity of the rock or rhyolite contained in the mixture, whereas the alunite present is decidedly changed physically and its specific gravity is very materially altered. This change in the relative specific gravity of the two constituents affords the basis for an easy mechanical separation.

The preferred method of carrying out the process is as follows:

The alunite, as mined, is reduced to say one-quarter inch size or finer, by any suitable means, such as a crusher and reducing rolls. The size of the particles of the reduced material may be widely varied, depending upon the character of the mined alunite, the output desired, and the condi- Specification of Letters Patent.

Patented Qli'ano 1155, rate.

Application filed November 13,1915. Serial No. 61,26'F.

tions of the subsequent roasting or calcining operation. The finer the reduction, the greater the dust loss in calcination. @n the other hand. the time required for calcination increases with the coarseness of the material. Having in View these considerations, it will usually be preferable to reduce to as nearly one-quarter inch size as possible, and to charge into the calcining furnace the particles of this size together with the accompanying fines, without any material or ex.- cessive quantit of coarser particles.

The crushe product, screened to reject the particles-of excessive size, may be fed into any suitable roasting or calcining kiln, preferably an inclined rotary kiln of the kind used in cement practice and which is fired with any suitable fuel, as, for instance, oil, gas, or pulverized coal. If it is desired to completely calcine the alunite, the kiln should be of such length and should have such a pitch as to allow the material to remain in the kiln for a eriod of time sufficient for its complete ca cination. The time of travel of the charge in the kiln from the upper feed end to the lower discharge end thereof will, of course, depend upon varying conditions, prominent among which are the size of the particles to be charged and the temperature employed. I have found, in commercial practice, that good results are obtained when the material charged is of one-quarter inch mesh with the accompanying fines and when the time of travel through the kiln is'from two to three hours. The temperature should be such as to heat the product before it is dischar ed from the kiln to from 800 C, to 1200 In general, a temperature of about 1000 C. is preferred, for the reason that, at that temperature, complete calcination of the alunite ma be obtained without danger of driving 0 by volatilization the potash contained 1n the alunite.

The calcined or roasted charge issuing from the kiln contains the rhyolite or native rock practically unchanged in specificgravity and insoluble in water. The orlgmal alunite, on the other hand, has been converted into a porous material conslstmg of alumina, insoluble in water, and potassium sulfate which is soluble in water.

In this condition, the calcined or roasted roduct can be separated mechanically, by dry or wet methods of separation, so to llllft remove from it the associated rhyolite or native rock. Thus, the separation can be effected by water jigs, air jigs, concentrating tables, flotation apparatus, or like well known expedients for the separation of materials of different specific gravities, and, accordingly, I do not confine myself, in the practice of the invention, generically considered, to the use of any particular separating device or method.

I have found it particularly advantageous,

however, to effect the mechanical separation of the constituents of the calcined-mixture, by admitting it into a pressure tank containing a body of water sufiicient in amount to permit of the dissolving out of substantially all of the potash. This pressure tank is preferably equipped with a stirring device of such a character as to keep all of the material in suspension and in motion, and the quantity of water employed is sufficient to give a saturated solution at say 90 C. allowance being made for such additional water as may result from the condensation of steam in those instances where live steam is admitted for the purpose of heating the contents of the pressure tank. The digestion is carried out at a pressure of preferably 50 to pounds to the square inch, although this pressure may be varied within wide limits, and may be as low as twenty pounds to the square inch. The necessary pressure may be produced by heating the contents of the pressure tank in any suitable way, as, for instance, by means of a steam jacket applied to the pressure tank, or by live steam admitted through perforated steam pipes or coils located within the pressure tank and supplied from without by a current of steam. It will usually be found that at the end of say one hour, the water has extracted almost all of the potassium sulfate from the calcined mass. Particular care should be taken that the amount of water employed shall be suflicient to maintain in solution all of the potassium sulfate which has been extracted, even thoughthe temperature of the solution should subsequently'drop to as low as say 90 C. The purpose of this is to provide for a sufficient drop in temperature in the solution to permit it to be filtered without depositing any part of its potash content in the filter press. During this treatment, any lumps of alumina present in the charge are for the most part broken up, so that practically all of the alumina contained in the charge is held in suspension by the ,water or can easily be kept in suspension by the stirring operation,

while the heavier rhyolite or native rock settles out.

In actual practice, I have found it convenient to blow the charge from the digester into a separating tank, in which the steam is released. From the separating tank, the

liquid and solid contents flow by gravity into a box provided with a V-shaped bottom and located directly beneath the separating tank. The V-shaped bottom of the box referred to is inclined at an angle of say 15 and contains a screw conveyer which carries the heavier particles of rhyolite or country rock settling on the bottom out to the waste dump. The material in suspension and which does not settle to the bottom of the tank, overflows to storage tanks, from which the solution of potassium sulfate may be filtered, decanted, or otherwise removed for separate recovery of the potash.

Having thus described my invention, what I claim is: I

1. The method of separating rhyolite or the associated rock or gangue from alunite, which comprises lowering the specific gravity of the alunite by a roasting or calcining operation which does not materially affect the specific gravity of the rock or gangue, and then separating by gravity the rock or gangue from the calcined alunite of the roasted product; substantially as described.

2. The method of separating rhyolite or the associated rock or gangue from alunite. which comprises crushing the mixture and roasting or calcining it under conditions which will lower the specific gravity of the alunite without material lowering the specific gravity of the rock or gangue, and then separating by gravity the rock or gangue from the calcined alunite of the roasted product; substantially as described.

3. The method of separating rhyolite or the associated rock or gangue from alunite, which comprises crushing the mixture to substantially one-quarterinch mesh, then calcining or roasting it in a rotary inclined kiln at a rate and temperature sufficient to lower the specific gravity of the alunite without materially lowering the specific gravity of the rock or gangue, and then separating by gravity the rock or gangue from the calcined alunite of the roasted product; substantially as described.

4. The method of separating rhyolite or the associated rock'or gangue from alunite, which comprises crushing the mixture to substantially one-quarter inch mesh, then calcining or roasting it in a rotary inclined kiln at a rate and temperature sufficient to lower the specific gravity of the rock or gangue, the temperature being maintained sufiiciently low during the calcining or roasting operation to avoid any substantial volatilization of the potash, and separating by gravity the rock or gangue from the calcined alunite of the roasted product; substantially as described.

5. The method of separating rhyolite or the associated rock or gangue from alunite. which comprises lowering the specific gravity of the alunite by a roasting or calcining operation which does not materially affect the rock or gangue, of lowered specific gravthe specific gravity of the rock or gangue, ity-from the undissolved calcined alunite of subjecting the product of the roasting or the roasted product; substantially as de- 10 calcining operation to an extraction operascribed.

5 tion to remove therefrom the'soluble potash In testimony whereof I affix my signature.

salt and thereby further disintegrating the product of calcination, and finally separating CARL F. HAGEDORN. 

